Sijinkumar A.V.,National Institute of Oceanography of India |
Sijinkumar A.V.,Government College Kasaragod |
Nath B.N.,National Institute of Oceanography of India |
Guptha M.V.S.,National Institute of Oceanography of India |
And 2 more authors.
Boreas | Year: 2015
The aragonite compensation depth (ACD) fluctuated considerably during the last glacial until the Holocene with a dominant pteropod preservation spike during the deglacial period, which is prominently seen in three well-dated cores covering the Andaman Sea, northeastern Indian Ocean. The precise time period of the preservation spike of pteropods is not known but this knowledge is crucial for stratigraphical correlation and also for understanding the driving mechanism. Isotopic and foraminiferal proxies were used to decipher the possible mechanism for pteropods preservation in the Andaman Sea. The poor preservation/absence of pteropods during the Holocene in the Andaman Sea may have implications for ocean acidification, driven by enhanced atmospheric CO2 concentration. Strengthening of the summer monsoon and the resultant high biological productivity may also have played a role in the poor preservation of pteropods. The deglacial pteropod spike is characterized by high abundance/preservation of the pteropods between ∼19 and 15cal. ka BP, associated with very low atmospheric CO2 concentration. Isotope data suggest the prevalence of a glacial environment with reduced sea surface temperature, upwelling and enhanced salinity during the pteropod preservation spike. Total planktic foraminifera and Globigerina bulloides abundances are low during this period, implying a weakened summer monsoon and reduced foraminiferal productivity. Based on the preservation record of pteropods, it is inferred that the ACD was probably deepest (>2900m) at 16.5cal. ka BP. The synchronous regional occurrence of the pteropod preservation spike in the Andaman Sea and in the northwestern Indian Ocean could potentially be employed as a stratigraphic marker. © 2014 Collegium Boreas.
Ghosh S.M.,Government College Kasaragod
Journal of Entomological Research | Year: 2012
Glyptapanteles obliquae (Wilkinson) is a promising biocontrol agent of Pericallia ricini Fab., a polyphagus pest attacking a wide variety of crop pests, including Diacrisia obliquae, Diacrisia obliquae confusa, Amsacta sp etc. Super parasitism is very common and up to 50 eggs were laid in the body cavity of a host larva. Under laboratory conditions 100% parasitism of the host occurs. Egg soon after oviposition measures 0.13 ± 0.02 mm in length. At 72 hours after oviposition the egg attains a length of 0.37 ± 0.06 mm and a width of 0.1 ± 0.02 mm. First instar larva appears 4 days after oviposition and measures 0.4 ± 0.04 mm in length and with a width of 0.18 ± 0.02 mm. The mandible measures 0.046 ± 0.003 mm in length and with a width of 0.019 ± 0.001 mm. The fully formed second instar larva measures 4.12 ± 0.5 mm in length It is without a sclerotised mandible. The third instar larva is hymenopteriform and measures 3.3 ± 0.4 mm in length. The larva has a well sclerotised mandible. Molting of the second instar to third instar takes place at the time of emergence of the parasitoid larva from the host body. This protects the remaining second instar parasitoid larva that are still developing inside the host larva from severe damage that might be caused by the mandibles of the molted third instar larva. It is an important parasitoid adaptation evolved for the gregarious life.
Bhattacharyya A.,Birbal Sahni Institute of Palaeobotany |
Sandeep K.,Mangalore University |
Sandeep K.,Government College Kasaragod |
Misra S.,Birbal Sahni Institute of Palaeobotany |
And 6 more authors.
Environmental Earth Sciences | Year: 2015
Vegetational history vis a vis climate change during the past 3100 cal. years BP was deciphered from pollen data supplemented with magnetic susceptibility and particle size data for a 2.5 m long sediment core from Pookot Lake, Kerala, southern India. Pollen data suggest a mixed assemblage of upland tropical elements and wetland mangrove taxa. The presence of trace amounts of pollen grains of montane taxa like Betula,Pinus and Alnus points to their long distance dispersal. Pollen grains of Ixora, Syzygium,Symplocos, Moraceae and Arecaceae that represent tropical vegetation were also recovered, indicating modern vegetation in and around Pookot Lake. Mangrove elements are mostly represented by species of Rhizophora and Ceriops decandra along with other taxa. High-rainfall periods are characterised by high sand % and low clay % and vice versa. The pollen data correspond well with magnetic susceptibility and particle size data. The data obtained suggest three broad phases of climate, with minor oscillations, during the past 3100 cal. years BP: (1) wet climate during 3100–2500 cal. years BP; (2) dry climate spanning a long period that ended around 1000 cal. years BP; (3) amelioration in climate after 1000 cal. years BP, reflected in the presence of luxuriant vegetation and high magnetic susceptibility values. © 2015, Springer-Verlag Berlin Heidelberg.
Ghosh S.M.,Government College Kasaragod
Journal of Entomological Research | Year: 2011
Meteorus species, a larval parasitoid of Pericallia ricini Fab. oviposits in I st, 2 nd ,3 rd and 4 th instar larvae of P. ricini. It completes its life stages with three larval instars. When second instar larva of P. ricini was given as host, the parasitoid completed its life cycle in 16.5 ± 1 day at 28° C. When 50 second instar larvae of P. ricini were provided to ten adult female parasitoid, 64% parasitism was noted in one hour with successful adult emergence of 54%. When second instar larvae of Corcyra Cephalonica smeared with crude Kairomones of Pericallia ricini were given as host to Meteorus sp. 44% parasitism was noted with 28% successful adult emergence. When second instar larvae of C. Cephalonica were given without Kairomones of P. ricini none of them were parasitised. When the parasitoid was reared in second instar larva of its unnatural host Corcyra cephalonica using the crude Kairomone extract of its natural host P. ricini , its life cycle was completed in 21 ± 1 day at 28°C. The total duration of immature stages of the parasitoid is completed in 16.45 ± 1.06 days at 28°C when reared in its natural host, P. ricini. The cocoon of Meteorus sp. is characteristic and it hangs from twigs leaves etc. by a fine thread, often several inches long. When Meteorus sp. was reared in unnatural host C. Cephalonica the cocoon develops inside the larval gallery of C. Cephalonica and lacks the suspending thread. In the field it is hyperparasitised by Eurytoma braconids Ferriere (6.4%), Aphanogmus manilae Ashmead (3.2%), and by Brachymeria sp. (11.3%).
Warrier A.K.,Mangalore University |
Shankar R.,Mangalore University |
Sandeep K.,Mangalore University |
Sandeep K.,Government College Kasaragod
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2014
Over the years, several proxies have been developed to reconstruct rainfall variability. However, most rely on indirect approaches to provide qualitative paleorainfall estimate. In an attempt to obtain a more direct measure of paleorainfall, Shankar et al. (2006) explored the rock magnetic properties of lake sediments from Thimmannanayakanakere (TK) in tropical southern India. They proposed the use of magnetic susceptibility as a proxy for rainfall in the tropics. Warrier and Shankar (2009) provided geochemical evidence in support of this proposition. Here, sedimentological and carbonate data is provided as further evidence to bolster Shankar et al.'s (2006) proposition.High (low) values of χlf indicate high (low) rainfall in the region of TK during the past 3700years. Particle size variations suggest that the sand % was high (low) during arid (humid) periods, when the TK lake level was low (high). Hence, a negative correlation is documented between sand % and χlf along with other rock magnetic parameters. HIRM (an indicator of magnetically "hard" minerals like haematite and goethite) is suggestive of a relatively arid climate; the high (low) HIRM values in TK sediments indicate arid (humid) conditions. For this reason, sand % is positively correlated with HIRM. By contrast, fine silt and clay contents are low during low-rainfall periods and vice versa. Thus, both fine silt and clay contents are positively correlated with χlf and other rock magnetic parameters, but negatively correlated with HIRM. Magnetic minerals reside principally in the fine silt fraction of TK sediments as evidenced from the positive correlation between fine silt content and magnetic susceptibility. Carbonate content too is indicative of paleorainfall conditions, being high (low) during arid (humid) climatic conditions. Based on the χlf, sand % and carbonate % data, we have inferred lake level variations in TK during the past 3700years. © 2013 Elsevier B.V.